acids. The following table gives the various physical proper-
tics, solubility, melting-point, and dissociation constant K of the
tu'o pairs of acids.
Mnleie . .
much less soluble, very soluble, much less soluble.
sublimes at 200° 80°
Urea. In addition to the method described in the prepara-
tion, urea may be obtained by the oxidation of anhydrous
potassium ferrocyanidc with potassium bichromate (Williams),
or manganese dioxide at a red heat, or by the action of per-
manganate on a cold solution of potassium cyanide (Volhard).
It has been synthesised by the action of ammonia on (i) phos-
gene, (.i) urclhane, (3) cbloroformic ester, and (4) ethyl carbonate.
1. COO, i 4NII.,-- NIIjj.CO.NIIo I 2NIJ4C1.
2. Niucoor.,!!,, i
^. ('1C(K)('! Ir, I 3
4. CO(()(!.,! hj., | 2
NIUCO.NIIo -f C,Ilr/)II.
NIUCO.NIIo H- CJIf.OH I NII4C1
NIUCO.NIIo -I- 2CoHrjOII.
also (5) by'the action of dilute acid on cyanamidc, and (6) by
heating guanidine with dilute sulphuric acid or baryta.
S. CNNIL I- 11,0 - NIUCO.N1U
(>. Nil :C(NIL,).2 i II..O ~ NIIo.CO.NIIa -! NH3.
The synthesis of urea by Wohler in 1828 is usually regarded
as a. tiu:ning-point in tin; history of organic chemistry, when
organic compounds ceased to be merely products of a vital force,
associated with living animals and plants. They now assumed
for the first time an independent role as substances capable of
synthesis by ordinary chemical means. In point of fact this is
not strictly true, for Scheele had prepared oxalic acid, only
previously known in wood sorrel and other plants, from cane
sugar, and Dobereincr had obtained the formic acid of ants by
the oxidation of tartaric acid. The formation of urea offers an
interesting example of intramolecular change of which many
cases are now known. See the formation of benzictine from